1. Field of the Invention
The present invention relates to an improvement of a liquid leakage sensor for reliably detecting leakage of water, an acid solution, an alkaline solution, or other liquid that is electrically conductive, or leakage of alcohol, thinner, benzene, or other organic liquid that has dielectric properties, without being affected by bubbles.
2. Description of Related Art
Liquids are typically supplied through pipes to equipment in manufacturing plants. This requires the use of numerous joints and couplings to connect sections of pipe, and leakage of liquid from these joints is common. Depending on the type of liquid being used, regular manual inspection is required to check for leakage. Typical liquid leakage detection methods include conductive and volumetric techniques. Japanese Examined Patent Application Publication (kokoku) 4-70572 teaches a liquid leakage sensor technology for reliably detecting liquid leakage by emitting light from a light source to a filter that turns transparent when it absorbs liquid, producing a change in light transmitted or reflected by the filter when there is liquid leakage. This change in transmitted or reflected light is used to reliably detect liquid leakage.
FIG. 1A illustrates the principle of this conventional reflection type liquid leakage sensor 20. A test paper and case holder 4 of which the bottom 4a is coated black is fastened by a screw or other fastener 6 to floor 1, and a white test paper (or cloth or synthetic resin) 8 is placed flat over bottom 4a. The bottom 4a is also a reflector. A case 12 of which the bottom 12a is transparent or semi-transparent is inserted to holder 4. A light source 14, photodetector 16, and comparator or other detection means 18 are together housed inside the case 12 and connected by way of cable 26 to the outside of the case 12.
It should be noted that the case 12 also functions as a dustproof and water-resistant cover. However, to facilitate penetration of leaked liquid 2 to the reflection area 8b in the middle of paper 8, and shorten the liquid leakage detection time, a gap 10 is disposed between paper 8 and the case bottom 12a. This gap 10 is preferably no more than several millimeters in order to avoid contamination by dust and other foreign particulate, and to stably detect light reflected from paper 8 without also detecting external light noise. Replacing the paper 8 and installation are also made easier by constructing the filter so that the reflector 4a and case 12 are removable. It is also not generally possible to identify the source of liquid leakage. As a result, the paper 8 is also preferably round so as to respond more quickly to liquid leakage from any direction.
A liquid leakage sensor 20 thus comprised emits light 22 from the light source 14, which is typically an LED, infrared laser diode, or optical fiber, to continuously monitor white reflected light 24 from the paper 8 by means of photodetector 16. However, when leakage 2 occurs at the floor 1, leaked liquid 2 gradually penetrates from contact area 9 to the reflection area 8b of paper 8, and the contact area 9 of paper 8 turns from white to transparent due to liquid absorption. Because the reflector 4a below the paper 8 is black, the color of the paper 8 changes from white to black in the contact area 9. Light 22 from the light source 14 is thus absorbed by the reflector 4a, significantly reducing the amount of light 24 reflected to photodetector 16. The detection means 18 thus detects this change in reflected light, and senses liquid leakage.
The following problems not initially expected to occur with a conventional optical liquid leakage sensor as described above remain to be solved.
(A) When the holder bottom 4a is level to the floor 1 and the case bottom 12a is also substantially level, a high pressure line or large-diameter pipe bursts and a large volume of liquid leaks at once, the entire circumference of the bottom of case 12 is submerged in liquid at substantially the same time. When the leaked liquid 2 then penetrates gradually from the outside edge of the paper 8 toward the inside, the air in the gap 10 between holder bottom 4a and case bottom 12a becomes trapped (although part of the air escapes outside the case 12 as a bubble) in the center of the gap 10 and surrounded by the liquid. As shown in FIG. 1B, this bubble becomes trapped in the center of the reflection area 8b, preventing the reflection area 8b from turning transparent no matter how much time elapses. As a result, it is not possible to detect that a large volume of liquid has leaked.
(B) Large numbers of flat holders having a level bottom 4a are currently in use. Replacing each of the holders 4 fastened to floor 1 would require a massive amount of time, and is substantially impossible.
(C) In addition, paper 8 is a consumable and is thrown away each time liquid is detected. It is therefore preferable to be able to reuse the paper 8  less than  less than  or eliminate use of the paper 8 greater than  greater than .
It should also be noted that the advantages of the liquid leakage sensor using paper 8 as described above include a simple design, reliable operation, stability and resistance to tipping over because it is fastened to the floor by a screw or other fastener, and the ability to detect high viscosity liquids in a relatively short period of time. On the other hand, users that would like to simplify or eliminate the work involved with installing the holder on the floor and replacing the test paper would like a liquid leakage sensor that does not use such paper and does not require floor installation.
Various liquid leakage sensors that do not use such a test paper have been proposed. These typically emit light to the bottom of the case, and evaluate the presence of liquid leakage by means of the amount of reflected light. However, if the case bottom is tight to the floor, it is very difficult for high viscosity liquids to penetrate to the middle of the case bottom. This means that the gap between the floor and the case bottom must be at the smallest at least 2 to 4 mm, which is significantly greater than in a sensor using paper as described above, and liquid leakage detection is not possible unless a large amount of liquid leaks so that the case bottom contacts the liquid.
Furthermore, if the case bottom is directly exposed to the floor surface, detection will be easily affected by the color of the floor surface, and when leaked liquid penetrates the sensor area, a large amount of unnecessary reflected light from the floor surface will also be detected, creating operating errors. Detection of liquid leakage based only on the amount of reflected light thus becomes unstable.
In addition, if the case is simply placed on the floor without fastening it to the floor, there is the danger of the case rising off the floor and even falling over.
The present invention was therefore conceived with consideration for the above-noted problems. An object of the invention is therefore to provide a liquid leakage sensor, paper for detecting liquid leakage, and a holder for detecting liquid leakage whereby liquid leakage can be stably and reliably detected without leakage detection being affected by bubbles even when a large volume of liquid leaks at one time.
A further object of the present invention is to provide a liquid leakage sensor, paper for detecting liquid leakage, and a holder for detecting liquid leakage whereby leakage of volatile liquids presenting the danger of flammable explosion can be remotely, safely, and reliably detected while taking care to prevent explosion and without leakage detection being affected by bubbles even when a large volume of liquid leaks at one time.
A yet further object of the present invention is to provide a liquid leakage sensor having a tilt detection function that does not use paper and can reliably, quickly detect liquid leakage even when the leaked liquid does not contact the case bottom.
To achieve this object, the present invention relates to a liquid leakage sensor comprising a white test paper that is made transparent by absorption of leaked liquid; a paper holder for holding level a test paper placed therein with the bottom of the paper holder forming a reflector; a case inserted to this holder and having a transparent or semi-transparent bottom; a light source for emitting light to the test paper through the transparent or semi-transparent bottom; a photodetector for detecting light reflected from the holder bottom; and a detector for detecting liquid leakage based on data from the photodetector. The light source and photodetector are housed together inside the case. A gap is formed between the holder and case so that leaked liquid penetrates rapidly when leaked liquid contacts one edge of the paper.
To achieve the above object with a liquid leakage sensor thus comprised, an asymmetrical opening is formed asymmetrically to the reflection area in a middle part not including the outside edge and reflection area of the paper when the shape of the paper is circular or noncircular so that a bubble is not trapped in the reflection area of the paper that is detected by the photodetector when a large volume of liquid leaks at once.
The present invention also relates to a liquid leakage sensor having at least one reflection plane able to contact leaked liquid, a light source, and a photodetection means. In this case, the object of the invention is achieved by projecting light to the reflection plane from the light source; detecting light reflected from the reflection plane by a plurality of photodetection means; applying an operation to photodetection means output to determine a brightness pattern distribution of the reflected light at a specific period; and determining the presence of liquid leakage from variation in the brightness pattern distribution of the reflected light.
The invention further relates to a liquid leakage sensor having at least one reflection plane able to contact leaked liquid; a case having a transparent or semi-transparent bottom; a light source for emitting light; a first light transmitting means for guiding light emitted from said light source to said reflection plane through the transparent or semi-transparent case bottom; a second light transmitting means for detecting and transmitting reflected light from the reflection plane; and a photodetection means for detecting light from said second light transmitting means.
A liquid leakage sensor thus comprised achieves an object of the present invention by forming an optical path from an end of the first light transmitting means and an end of the second light transmitting means housed inside the case. The second light transmitting means has a plurality of light transmitting elements whereby light is transmitted so that reflected light photodetection positions can be mutually distinguished. Positions at which reflected light is detected by the plural photodetection elements are converted at the other end of the second light transmitting means to electrical signals so as to be mutually distinguishable. Output of the photodetection means is then processed to determine at a specific period a brightness pattern distribution of the reflected light. Presence of liquid leakage is then detected from change in the brightness pattern distribution of reflected light.
An object of the present invention is further achieved by means of liquid leakage sensor having a first liquid leakage sensor and a second liquid leakage sensor. The first liquid leakage sensor has a first detection means having at least two reflection planes able to contact leaked liquid formed with a gas layer or a leaked liquid permeation layer disposed therebetween in the direction of light transmission; at least two light sources and photodetection means disposed on the same side of each reflection plane; emitting light from a first light source at an incidence angle equal to or greater than a critical angle to a first reflection plane nearest said light source; detecting reflected light from said first reflection plane by means of a first photodetection means; and processing said photodetection means output to detect liquid leakage. The second liquid leakage sensor has a second detection means for emitting light from a second light source at an incidence angle less than said critical angle to a reflection plane other than said first reflection plane, detecting reflected light from a reflection plane other than said first reflection plane by means of a second photodetection means, and processing said photodetection means output to detect liquid leakage.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.